Electron-tube system



Jul 13, 1926.

J. SLEPIAN ELECTRON TUBE SYSTEM my. a.

Filed Jan. 51 F/g, l

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ATTORNEY Patented July 13, 1926.

uNrrEo STATES 1,592,388 PATENT orrica.

i a I i 1 JOSEPH SLR PI, OF WILIINBBURG, IENNSYLV LNIA, ABQIGNOR '10 WESTINGHOUSE ELECTRIC MANUFACTURING CQMPM, A COmATION OI PENNSYLVANIA.

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Application filed January 31, 1921. zit-mono. 441,121.

My invention relates to means for preventing ower loss in electron tubes and, more particularly, to means for causing the voltage impressed upon the tube and the current flowing therethrough to vary 1n a squaretop manner.

[One object of my invention. is to increase the efliciency and rating of an electron tube by decreasing the amount of heat produced within the tube.

Another object of my invention is to provide sim 1e and durable apparatus for ,producingt e current and t e voltage waves above mentioned.

Formerly, where the voltage impressed upon, and the current passing through, the electron tube was of sinewave sha e or other form in which the current and t e voltage Were not of the square-top t pe, there was considerable loss in the tu e because of heating efiects. These heatin efi'ects reduced the effective rating of t e tube and operated largely to reduce its efliciency.

In order to make my invention more clearly understood, I have shown, in the accompanying drawings, systems for carrying the same into practical efi'ect, with the understanding that the arrangement of the several necessary elements may be varied without departing from the spirit of the invention.

In the drawings:

Figure 1 diagrammatically illustrates an embodiment of my invention in which power is taken from the plate circuit of the tube to supply the primary of an induction furnace.

Fig. 2 is a diagram showing the variations in voltage of the tube.

Fig. 3 is a diagram illustrating the variation in current corresponding to the volting a filament element 2, a grid element 3 and a plate element 4. The filament element 2 is heated by means of a suitable A battery 5 which may be regulated to furnish the desired amount of current. The plate circuit is supplied from a direct current source 6 of hig potential, through tapping the mains. In this case, the high-potential, direct-current generator 6 takes the place of the customary B battery but it is to be understood that any high-potential, direct-current source may be used.

In the grid circuit ofthe tube 1 is a G battery 7 the leads from the positive and .ne ative terminals of which are connected to rushes 8 and 9, respectively. The brushes 8 and 9 are'adapted to bear against a higheed commutator member 11 diagrammatica 1y illustrated. The high-speed commutator member 11 comprises two sections, a conducting section 12 and an insulating section 13. A brush 14 is adapted to continuously bearagainst the conducting section 12,- and is connected to the grid 3 of the electron tube 1. The hi h-speed commutator 11 allows potential rom either. the positive or the ne ative side of the C battery 7 to be applie to the grid 3 and, in its rotation,

both positive and negative potential will be applied to the grid.

In the plate circuit of the electron tube 1 is located an inductance 15 that operates to furnish the primary current for an induction furnace 16 that is die rammatically illustrated in section. The in uction coil 15 induces currents in the furnace 16 which heat the char The internaI heating in an oscillator tube, or in any other translating device, is a summation' of the instantaneous PR losses. If, therefore, the internal resistance of an oscillator tube should he suddenly changed from a negligible small value to an extremely large value, the tube will either transmit current with a negligibly small voltage drop across its terminals and with a negligibly small PR loss, or it will not transmit any material quantity of electricity, the resistance drop across the terminals of the tube being cillator tubes thus occurs almost entirely dur- .ance shunted by resistance. Evi

in the intervals when the resistance has a fimte value, that is, when it is changing from an extremely low value to an extremel high value, or vice versa, and, with this thought as a starting point, I have devised a method and means w ereby ve considerable economies in operation, an increased ratings of already existing tubes, may be obtained.

For the theory of operation of m system, a study of vthe curves shown in igs. 2, 3 and 4 will be of assistance. The voltage of the grid 3 is varied in a uare-top manner, as indicated in Fig. 4. en the grid is positive, the impedance of the tube 15 negligibly small and hence the voltage across the tube terminals is negligibly small, but when the grid is negative, the impedance of the tube is extremely high and hence the voltage across the tube is substantially that of the direct-current source 6, all as indicated by the curve shown in Fig. 2. The current is displaced in respect to the voltage so that, w en the voltage is at a minimum, the current is at a maximum and vice versa, as explained hereinabove and illustrated in Fig. 3. This relationship will minimize heating in the tube. However, it is to be understood that the ideal waves and conditions diagrammatically shown can on] be approximated.

ince the direct-current source 6 furnishes a constant impressed -,electromotive force,

and since the tube takes alternately substan-- tially all of said electromotive force and substantially none of it, as. indicated in Fig. 2, the voltage impressed upon the external load circuit has a square-topped formation substantially similar to the curve shown in Fig. 3. Since the tube is a unidirectional conductor, the current in the work circuit cannot reverse and hence must fall to zero during the intervals in which the tube has an extremely high impedance. As is wellknown, a square-topped unidirectional wave, such as that shown in Fig. 3, may be resolved, by the Fourier series, into a directcurrent component, a fundamental sine wave, and a series of harmonics, usually of diminishing m itudes, the even harmonics being absent i the two half cycles are symmetncal.

For many purposes, the above wave shapes are not permissi 1e, and net works that will take voltages as above indicated with most of the direct-current component lacking and which will operate as actual load circuits are necessary to the proper functioning of my system. One net work which will take such voltages and currents is a high reactently, if a sqipare-top current is sent through this com ination, the direct-current component will pass through the reactance, while the alternating-current component will practically all pass through the resistance, giving a square-top voltage wave.

A transformer o crating under load has anequivalent circuit similar to a reactance shunted b resistance. In Fig. is shown the equiva ent circuit of a transformer having'small leakage-flux reactances 17 and 18, as indicated. The load is indicated by the resistance 19. If the leakage-flux reactances are not too large the transformer will operate in a manner similar to high reactance shunted by resistance. In Fig. 1, the primary induction coil 15 of the induction furnace 16, operates to supply the power to a secondary that is, in fact, the char to be heated or the crucible containing t e charge, and hence, a circuit operatin with such a load will be practicable with my flat-top-wave-generator tube.

In the operation of the system shown in Fig. 1, the filament 2 is caused to emit electrons, and the grid 3 has its potential changed by the rotation of the high-speed commutator member 11. The conducting portion 12 of the commutator member 11 comes alternately into contact with the brush 8 and the brush 9. The potential on the grid 3 of the tube 1 is, therefore, changed in a square-top manner. The high-potential direct current from the source 6 supplies the direct current for the late circuit, and this direct current, in com ination with the current resulting from the change in voltage of the grid 3, will give a voltage curve for the plate circuit corresponding to the curve shown in Fi 2 and a current curve corresponding to t e curve shown in Fig. 3. The inductance 15 operates as the primary of a transformer the secondary of which is the char e in the induction furnace 16 or the cruel le in which the char e is contained. This transformer is one wit small leakage reactance, and, therefore, the equivalent circuit of the transformer will operate as a high inductance shunted by resistance. Hence, the conditions necessary for efficient operation of the tube are present.

It is to be understood that many other alternating-current translating devices may be used in place of an inductlon furnace in my system, and that the fundamental sine wave may be taken from the square-top wave. This induces heat generation in the external circuits, but heat production within the tube is greatly reduced over present practice, and thus, the rating of the tube may be radicallyincreased.

In the modification illustrated in Fi 6 is shown an electron tube 21, having a %lament element 22, a grid element 23, and a plate element 24. The filament is heated by a suitable A battery 25, the amount of current flowing being controlled to produce the proper electron emission. A C battery 26 applies negative potential to the grid 23.,

In the plate circuit of the tube is located a B battery 27 for furnishing direct current to the plate circuit.

Located within the plate circuit is a battery 28 in series with a rectifier 29, and, in parallel with the battery 28 and the rectifier 29, is a battery 30 and a rectifier 31. The rectifier 29 prohibits current passing through that branch of the circuit except in one direction, and the battery 28 opposes, by its potential, the flow of current in that direction. Therefore, if current will flow through the circuit containing the battcry 28 and the rectifier 29, the voltage in the plate circuit must be built up to overcome the potential of the battery 28, at which time the current will break through, giving a square-top voltage. Likewise, in the circuit containing the battery 30 and the rectifier 31, the potential of the battery 30 is opposedto the electromotive force in the plate circuit. The rectifier 31 allows current to flow in but one direction which is exactly opposite to that of the rectifier 29. Thus, in the other half of the cycle of the alternating current, the current may break through the rectifier 31 and the battery 30 but only when the electromotive force of the plate circuit has been built up to a point to overcome'the potential of the battery 30. The current then breaks through, giving a square-top volt-age. Therefore, these batteries and rectifiers operate to insure that the current, flowing through the portion of the circuit containlng them, induces a square-top voltage.

In parallel with these two circuits containing a battery and rectifier each, is an inductance 32- located in inductance relation to an inductance 33 in the grid circuit of the tube. When a difference of potential is impressed upon the divided circuit 29-31, in a direction opposed to the battery 28, it will cause current to flow in the coil 32 and will build up a field in this coil. When this difference of potential reaches such a value that it exceeds the potential of the battery 28, the direction of electromotive force at the rectifier 29 is reversed and this rectifier changes its character from a great impedance to a practically nil impedance. Consequently, the electromotive force impressed upon thecoil 32, while current is flowing in the plate circuit, due to the conducting condition of the tube, rises abruptly to a. certain maximum fixed by the battery 28 and then is continued at that-maximum.

When the current in the plate circuit terminates, the field in the coil, 32 causes an electromotive force to be impressed upon the divided circuit 29--31. This electromotive force is in a direction opposed to the battery 30. Then it exceeds the electromotive force of the battery 30, the direction of electromotive force through the rectifier 31 is re- The relations between the currents in coil ing equations:

dt I at 32 and coil 33 are expressed by the followin which L 'and'L, are the self inductances,

M the mutual inductance, 1', and i the currents and E and E the electromotive forces in the respective coils. The current 1', is a constant and equal to zero because the grid circuit is an open circuit. Consequently, the second terms on the left-hand side of these equations are zero. Therefore, the e uations show that the electromotive forces 1 and E, bear a constant ratio but it has been shown by the above discussion that the electromotive force E rises abruptly to a certain value, continues constant, changes abruptly to a certain value of the opposite sign and again continues constant. Since the two electromotive forces have a constant ratio, the electromotive force E changes in this same square-wave fashion. This is the reason why, in discussing the current through, the divided circuit 29-31, it was stated that this current stops and starts abruptly. It will be seen, by considering the cycle of actions, just described, that this assumption is not arbitrary, but is a conseuence of the structure disclosed. It results rom the abrupt change in the conductivity of the rectifiers 29 and 31, when the direction of the electromotive force through them is reversed.

The output circuit of the tube 21 furnishes an illustration of the statement above, that many types of load beside that specifically described in connection with Figs. 1 and 5, may be used advantageously with a tube giving a square form of wave. The illustration chosen shows the application to a I load re uiring an alternating current corresponding to the fundamental frequency of the square-form wave but from which the direct current component and the more powerful of the harmonics must be excluded.

Within the plate circuit is located a frequency trap 34 comprising an inductance and a capacitance 36 in parallel, shunted by a resistance 37. This frequency trap 34 is resonant to the third harmonic and acts to absorb the energy of the third harmonic in accordance with well known principles of voltage resonance. A frequency trap 38,

comprising an inductance 39 and a capacity 40, in parallel, shunted by a resistance 41, 1s resonant to the fifth harmonic and absorbs the energy of that harmonic. Within the plate circuit is located an inductance 42 operating as the primary, of a transformer from which the output of the tube may be utilized. The inductance 43, shown inductively cou led to an inductance 42 and operating as t e secondary of the transformer, is located in a circuit carrying the load.

In operation, the tube 21 is adjusted to function as a continuous generator of oscillations, by reason of the feed-back transformer coupling 32, 33 between the plate ciremits electrons, and the flow of current in the plate circuit has its third and fifth harmonic removed by the frequency traps 34 and 38. In that portion of the circuit connected in parallel with the inductance 32, which functions as a primary of a transformer the secondary 33 of which is in the grid circuit, are located the two circuits connected in parallel and having a battery 28 and a rect1fier 29 and a battery 30 and a rectifier 31 res actively, as has been previously described. The rectifiers and batteries in each circuit are so arranged that current may flow through one branch in one direction only, and the electromotive force of any current which flows is opposed to the electromotive force of the battery in that branch, so that, when current does finally pass, the voltage will have been built up to such a high value that the current will break through 1n a square-top manner. This is true of the arallel connection except that current for t e other half of the cycle only passes.

.The inductance 32, connected in parallel with the batteries and rectifiers, insures that the grid 23 will be excited in a s uare-top manner, through the mutuality o inductance between plate and grid circuits. This causes the current output to remain of square top form and to correct any tendency for the higher harmonics of current to shift relative to the fundamental. The effective current flowing in the inductance 42, that operates as the primary of a transformer, the secondary of which is the inductance 43 located in the circuit carrying the fundamental frequency load, is substantially of sine-wave conformation. This causes a certain amount of loss of ener y in the external circuits but the added efiiciency of the tube more than compensates for this loss. It

will be unnecessary to discuss the passage of current through the transformer, comprising the primarg 42 and the secondary 43, since this has een fully explained in connection with the operation of what is,

shown in Fig. 1, taken in connection. with what is shown in Fig. 5.

It is evident that there will be losses apearing as heat in resistances 37 and 41 and in the parallel resonant circuits. These losses ma be large enough to make the theoretica efficiency of the whole system less than that of a similar transformer 42-43 fed by an ordinary regenerative vacuum-tube oscillator. Such a diminution in theoretical efliciency will often be more than counterbalanced by the circumstance that, with the square-wave-form system, the losses occur mainl outside the tube where provisions for issipating the heat can be provided more conveniently and inexpensively than inside the tube. cuit and the grid circuit. The filament 22 Since I have not shown all possible modifications of my invention that may. occur to those skilled in the art, I desire that my invention shall be limited only by the scope of the appended claims and the showing of the prior art.

I claim 1. An electron tube comprising a cathode, a plate, a grid, means causing the current in the plate circuit to be of square-top form. a primary of a transformer in the plate circuit, means operating as a secondary in inductive relation thereto and located in the grid circuit and a load operating as high reactance shunted by resistance.

2. An electron-tube system comprising an electron-emittingcathode, a plate element, a grid element, means in the plate circuit insuring that the plate current passing through that ortion of the circuit shall be of square-top cm and means coupling that portlon of t e plate circuit to the grid.

3. An electron-tube system comprising an electron-emitting cathode, a plate element, a grid element, means in the plate circuit for insuring that the plate current passing through that portion of the circuit shall be of square-top form, an inductance in parallel to that portion of that circuit and an inductance in the grid circuit in inductive relation to the first mentioned inductance.

4. An electron-tube system comprising an electron-emitting cathode, a plate element, a grid element, rectifiers in the plate circuit, batteries in the plate circuit and means coupling that portion of the plate circuit contaimng the atteries and the rectifiers to the grid so that the grid may be excited in a squaretop manner.

5. An electron-tube system comprising a plate element, a grid element, rectifiers in the plate circuit, batteries in the plate circuit, an inductance in parallel with that portion of the circuit containing the batteries and rectifiers and an inductance in the grid circuit in inductive relation to the first mentioned inductance'so that the grid will be excited in a square-top manner.

6. An electron-tube system comprising an electron-emitting cathode, a plate element,

a grid element, means in the plate circuit insuring that the plate current passing through that portion of the circuit shall be of square-top form, means coupling that portion of the plate circuit to the rid and circuits resonant to the harmonics o voltage and shunted by resistance in the plate circuit.

7 An electron-tube systemcomprising an electron-emitting cathode, a plate element, a grid element, means in the plate circuit insuring that the plate current assing through that portion of the circuit s all be of square-top form, an inductance in parallel with that ortion of the circuit, an inductance in t e grid circuit in inductive relation to the first mentioned inductance and circuits resonant to the harmonics of voltage and shunted by resistance in the plate circuit.

8. Anelectron-tube system comprising an electron-emitting cathode, a plate element, a grid element, rectifiers in the plate circuit, batteries in the plate circuit, said batteries and rectifiers' being so arranged that ourrent will flow through the portion of the circuit containing them in a square-top manner, means cou 'hng that portion of the plate circuit contaimng the batteries and rectifiers to the grid and circuits resonant to the harmonics of voltage and shunted by resistance in the plate circuit.

9. An electron-tube system comprising an electron-emitting cathode, a plate element, a grid element, rectifiers in the plate circuit, batteries in the plate circuit, said batteries and rectifiers being so arranged that current will flow through that portion of the circuit containing them in a square-top manner, an inductance in parallel with that portion of the circuit containing the batteries and rectifiers, an inductance in the grid circuit in inductive relation to the first mentioned inductance and circuits resonant to theharmonics of voltage and shunted by resistance in the plate circuit.

In testimony whereof, I have hereunto subscribed my name this 18th day of January, 1921.

J SLEPIAN. 

